Contraband is the rarest label in CS2, and it belongs to a single skin: the M4A4 | Howl. The skin was released in the Huntsman case in 2014, and Valve later found the artwork had been copied from an artist without permission. Valve replaced the art with a new design, removed the skin from the case, and gave existing copies the new Contraband rarity.
The label is a dark orange or amber colour, different from every other tier.
Why is the M4A4 Howl so expensive?
No new copies can ever be made. The Howl does not drop, cannot be unboxed, and cannot be produced by a trade-up contract. Every Howl in the game today already existed when the skin was pulled. Some have been deleted or sit in abandoned accounts, so the supply only falls. Demand stays high because the skin is famous and the M4A4 is a popular rifle.
StatTrak copies and Factory New copies are rarer still, and Howls with well placed stickers from old Major capsules can be worth many times a plain copy. Souvenir versions never existed, since the Howl came from a case rather than a map collection.
Is Contraband a real rarity tier or just a label?
It is a real tier in the game files, but it exists for one item and behaves differently from the others. The Howl does not fit the trade-up ladder as an output, and it is not in any drop pool. Some stickers were also affected by the same dispute and were removed, but only the Howl received the Contraband rarity. Treat Contraband as a footnote in the rarity system rather than a tier you can aim for.